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The word "polygraph" means "many writings" in graph form a simple definition that gets considerably more complicated when applied to the polygraph machine. About all that proponents and opponents of this device can agree on is that its operation involves as much art as science because it is the interpretation of graphs that counts.Few people anywhere claim that the machine better and somewhat incorrectly known as a lie detector is infallible. At best, it is what Frank Horvath, a professor of criminal justice at Michigan State University and a past president of the American Polygraph Association, calls "a diagnostic tool." At its worst, it traps people who are "truth tellers" by implicating them falsely.The machine measures a person's physiological reactions changes in heart function, respiration and perspiration to a carefully phrased series of questions that result in a computer printout similar to that of an electrocardiograph. Generally, a significant change in vital signs an increased heart rate, etc. indicates a person is lying.The exam is administered by a polygraph examiner trained to read the results and upon whose expertise the outcome depends. Depending on the reason for the test, the examiner can determine the worth of the exercise or rule the outcome inconclusive. At least 60 hours of college work or equivalent experience in police work are required for trainees. An examiner reviews with the test taker ahead of time the language employed to be certain no words are used that the subject does not understand. The examiner also establishes what is called a base line to determine the subject's normal nervous response, given that most people are anxious to some degree in such a setting at least for the first time. The nearest center locally is at the Maryland Institute of Criminal Justice in Millersville, which says three of the last 15-member classes have been filled. The school's next session begins Monday."Everything is relative," says Mr. Horvath, who supports polygraph exams as "the only method we have to investigate certain issues that happen to be of interest to a security organization." He points out that the object of the machine in employment screening is "not to [catch you] in a lie but to try to verify you have told the truth." A polygraph machine also is an investigative tool widely used by law enforcement for what Mr. Horvath calls "a specific-issue exam" to elicit information from a suspect by comparing the responses to questions deliberately introduced to obtain varying physiological reactions, depending on how the questions are phrased.A screening exam is different from a specific-issue exam, which is intended to find out if a person is guilty of a particular act. "Different kinds of questions are reviewed in advance," Mr. Horvath says. "Comparison questions provoke a response on your part against which is measured a possible response to one of the other questions. For instance, if I ask if your name is so-and-so, you would answer yes. I then ask if you stole $500 from the bank. If you didn't respond physiologically to either of these, that would mean you were telling the truth or were not responsible for the [stealing] procedure."Used correctly, he says, the machine detects deceptive behavior and, depending on the nature of the questions put to the test taker, can result in a confession on the part of a person under suspicion. Civil libertarians have objected to the polygraph machine on many grounds, one of which is the perception of it as a "fear machine" that it is so intimidating it can traumatize an individual into giving a false confession.To date, all that students of polygraphy seem to agree on across the board is the need for further research regarding the efficacy of a device that is banned by law for screening in most places of private employment but is virtually an everyday accessory in about 60 percent of law enforcement offices, Mr. Horvath says.Arguments about the machine's accuracy vary, with proponents claiming up to 90 percent accuracy when used for specific-issue exams."No question this is a strange field, and even in the scientific community there aren't too many people in the middle," Mr. Horvath says. "I'm willing to say we don't know whether the critics are right or not. Statistics are only part of the matter."The government regards polygraphy as so important that it sends nearly all federal examiners to be trained at a Department of Defense site in Columbia, S.C. The CIA has employed polygraph exams since the 1950s, but the FBI didn't begin doing security screenings of agents having access to confidential data until after revelations about Robert Hanssen's spy activities came to light.A polygraph test usually takes place in government agencies after a background check. At a minimum $200 each, it is considerably less expensive than a full-bore background check, which costs thousands of dollars. Examiners who are trained privately at one of the many national centers recognized by the American Polygraph Association pay upward of $4,000 for a 10-week course at the Maryland Institute of Criminal Justice, following which they are considered interns for six months, refining their technique on the job, says Bruce White, president of Axciton Systems Inc. of Houston, which also sponsors a training center.Some become specialists in such fields as pedophilia, gang homicides and even trucking to fully immerse themselves in the activities and language of those worlds.Manufacturers say technology is improving constantly. The most up-to-date versions have been digitized, using software that is less intimidating to the person being observed. Bruce White, a physicist who is president of Axciton Systems Inc. of Houston, says it soon will be possible for technology to very nearly eliminate the chance of using so-called "countermeasures" to cheat."A good exam is like a ballet. You don't even know it's occurring until it is over," Mr. White says, maintaining that "charts now contain much more science than they used to, but interrogation is the art and skill you never get really perfect. The art depends on the person; everyone has his own style."To date, his company and others have worked to answer the demand for less intimidating testing components. The old days are gone when a needle would visibly jump up and down on a page recording reactions. The present advanced systems use computers that generate silent signals and create what polygraphers call algorithms programmed calculations that help the examiner interpret results.Examiners, by and large, can catch people trying countermeasures "if they are attentive to the charts," Mr. White insists. "We have a motion channel on the chair to detect muscular movements that are timed specifically on comparison questions. You can see a person doing unusual things with the tongue or jaw muscles. Some people try to hold their breath, but they can't do it on all the traces at the same time."Suspects have tried pushing down hard on the sole of a foot at certain moments to throw off the sensors or put a tack in their shoe for the same purpose.A person may spend only about eight minutes on the machine itself, Mr. White says. Two other parts of the experience are a pre-exam interview and a post-exam resolution. If deceptiveness has been detected, the examiner will push for more information. The pre-exam interview determines what he calls the client's "mind-set bright versus simple-minded are handled differently."With a bright person, you want to be sure you don't inadvertently interpret statements too deeply. Say, in a homicide case, you are testing a husband who is innocent. If you ask, 'Did you cause the death of [your] wife?' in his mind he may feel contributory guilt thinking he should have been home. You have to be clear so there is no misinterpretation. So you ask, 'Did your hand pull the trigger?' That is part of the training."Psychologist Stan Adams of Portland, Ore., author of "The Complete Polygraph Handbook," says the Defense Department's center has instituted methods advanced enough to outwit the most sophisticated suspect someone such as a former CIA or FBI employee whose job was to investigate espionage and issues of national security and who would be familiar with all the countermeasure techniques."The examiner watches for movements, which the computer detects, and if you get movements too often, which is what typically happens, you know what a person is doing. Most people do it in a primitive way, so it is obvious," he says.Mr. Adams says one of the most consistently effective uses for polygraph machines is for what he calls post-conviction testing. "In the 1970s, a judge took the worse candidates for probation to agree to take the test every six months to see if they were re-offending. Compared to a control group, the results were impressive in terms of deterring people," he says.Therapists praise the method, and it saves money keeping people out of prison, Mr. Adams says."Even if you have taken a test before, the accuracy is still high. Habituation, surprisingly, doesn't reduce the accuracy. If someone committed murder 40 years ago, you may think related feelings aren't the same today, but what is going to happen is that person knows he still is facing prison," he says. His emotional responses will be consistent, Mr. Adams says.The key to making polygraphs work, he says, is "having something to lose in the process. Otherwise, you are not going to be as reactive."